thread-join returns the result of finished thread

* doc/lispref/threads.texi (Basic Thread Functions):
* etc/NEWS: Document return value of `thread-join'.

* src/thread.c (invoke_thread_function, Fmake_thread)
(init_main_thread): Set result.
(Fthread_join): Propagate signals, and return result.
(Vmain_thread): New defvar.

* src/thread.h (struct thread_state): Add `result' field.

* test/src/thread-tests.el (threads-join): Test also return value.
(threads-join-error): New test.
(threads-mutex-signal): Check for propagation of `quit' signal.

1 files changed, 17 insertions, 6 deletions

diff --git a/test/src/thread-tests.el b/test/src/thread-tests.el
index a447fb3914e..364f6d61f05 100644
--- a/test/src/thread-tests.el
+++ b/test/src/thread-tests.el
@@ -100,15 +100,24 @@
    (progn
      (setq threads-test-global nil)
      (let ((thread (make-thread #'threads-test-thread1)))
-       (thread-join thread)
-       (and threads-test-global
-            (not (thread-alive-p thread)))))))
+       (and (= (thread-join thread) 23)
+            (= threads-test-global 23)
+            (not (thread-alive-p thread)))))))
 
 (ert-deftest threads-join-self ()
   "Cannot `thread-join' the current thread."
   (skip-unless (featurep 'threads))
   (should-error (thread-join (current-thread))))
 
+(ert-deftest threads-join-error ()
+  "Test of error signalling from `thread-join'."
+  :tags '(:unstable)
+  (skip-unless (featurep 'threads))
+  (let ((thread (make-thread #'threads-call-error)))
+    (while (thread-alive-p thread)
+      (thread-yield))
+    (should-error (thread-join thread))))
+
 (defvar threads-test-binding nil)
 
 (defun threads-test-thread2 ()
@@ -197,7 +206,7 @@
 (ert-deftest threads-mutex-signal ()
   "Test signaling a blocked thread."
   (skip-unless (featurep 'threads))
-  (should
+  (should-error
    (progn
      (setq threads-mutex (make-mutex))
      (setq threads-mutex-key nil)
@@ -206,8 +215,10 @@
        (while (not threads-mutex-key)
          (thread-yield))
        (thread-signal thr 'quit nil)
-       (thread-join thr))
-     t)))
+       ;; `quit' is not catched by `should-error'.  We must indicate it.
+       (condition-case nil
+           (thread-join thr)
+         (quit (signal 'error nil)))))))
 
 (defun threads-test-io-switch ()
   (setq threads-test-global 23))